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Chapter 3: Top-Down Design with Functions and Classes. Problem Solving, Abstraction, and Design using C++ 6e by Frank L. Friedman and Elliot B. Koffman. 3.1 Building Programs with Existing Information. Analysis and design phases provide much information to help plan and complete a program - PowerPoint PPT Presentation
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Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Chapter 3: Top-Down Design with Functions and Classes
Problem Solving,
Abstraction, and Design using C++ 6e
by Frank L. Friedman and Elliot B. Koffman
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 2
3.1 Building Programs with Existing Information
• Analysis and design phases provide much information to help plan and complete a program
• Can start with data requirements to develop constant and variable declarations
• Use the algorithm as a first step in coding executable statements
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Case Study: Finding the Area and Circumference of a Circle
• Problem statement
Get the radius of a circle. Compute and display the circle’s area and circumference.
• Analysis– input is the circle’s radius– need calculation for the area– need calculation for the circumference
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Case Study: Data Requirements
• Problem ConstantPI = 3.14159
• Problem inputfloat radius // radius of a circle
• Problem outputfloat area // area of a circlefloat circum // circumference of a
circle
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Case Study: Formulas
• Area of a circle = radius2
• Circumference of a circle = 2 radius
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Case Study: Design - Algorithm
1. Get the circle radius
2. Compute the area of circle
3. Compute the circumference of circle
4. Display area and circumference
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Case Study: Design - Algorithm
1. Get the circle radius
2. Compute the area of circle2.1 Assign PI * radius * radius to area
3. Compute the circumference of circle3.1 Assign 2 * PI * radius to circum
4. Display area and circumference
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Listing 3.2 Outline of area and circumference program
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Listing 3.3 Finding the area and circumference of a circle
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Listing 3.3 Finding the area and circumference of a circle (continued)
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Case Study: Testing
• Radius of 5.0
• Should get area of 78.539…
• Should get circumference of 31.415...
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Case Study: Weight of Flat Washers
• Problem statement
You work for a hardware company that manufactures flat washers. To estimate shipping costs, you company needs a program that computes the weight of a specified quantity of flat washers.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 13
Case Study: Weight of Flat Washers
• Analysis– flat washer is like a small donut– need to know rim area, thickness, density– rim area will be computed from knowing the
washer’s outer and inner diameters.
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Case Study: Data Requirements
• Problem ConstantPI = 3.14159
• Problem inputsfloat holeDiameter // diameter of hole
float edgeDiameter // diameter of outer edge
float thickness // thickness of washer
float density // density of material used
float quantity // number of washers made
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 15
Case Study: Data Requirements
• Problem outputfloat weight // weight of batch of washers
• Program Variablesfloat holeRadius // radius of holefloat edgeRadius // radius of outer edgefloat rimArea // area of rimfloat unitWeight // weight of 1 washer
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 16
Case Study: Formulas
• Area of circle = radius2
• Radius of circle = diameter / 2
• Rim area = area of outer circle - area of hole
• Unit weight = rim area thickness density
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Listing 3.4 Washer program
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Listing 3.4 Washer program (continued)
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Case Study: Testing
Input datainner diameter of 1.2
outer diameter of 2.4
thickness of 0.1
material density of 7.87
quantity in batch of 1000
Should produceexpected weight of batch of 2670.23 grams
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3.2 Library Functions
• Goals of software engineering– reliable code– accomplished by code reuse
• C++ promotes code reuse with predefined classes and functions in the standard library
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C++ cmath Library
• Typical mathematical functions
e.g. sqrt, sin, cos, log
• Function use in an assignment statement
y = sqrt(x);
Function name
Function argument
Function call
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Example: sqrt Function
Square root function
Function sqrt as a “black box”
X is 16.0 Result is 4.0
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Listing 3.5 Illustration of the use of the C++ sqrt function
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Listing 3.5 Illustration of the use of the C++ sqrt function (continued)
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Table 3.1 Some Mathematical Library Functions
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Table 3.1 Some Mathematical Library Functions (continued)
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Looking Ahead• Could write own functions
– findArea( r ) returns area of circle of radius r
– findCircum( r ) returns circumference of circle of radius r
• Program to compute area and circumferencearea = findArea(radius);
circum = findCircum(radius);
• Washers programrimArea = findArea(edgeRadius) -
findArea(holeRadius);
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 28
3.3 Top-Down Design and Structure Charts
• Top-down design– process to break down complex problem into
smaller, simpler subproblems– similar to development of an algorithm
• Structure chart– graphical representation of relationship of
subproblems
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Case Study: Simple Figures
• Problem statementDraw some simple diagrams on the screen, e.g. a
house and a female stick figure.
• Analysis– house is formed by displaying a triangle
without its base, on top of a rectangle– stick figure consists of a circular shape, a
triangle, and a triangle without its base.– 4 basic shapes: circle, base line, parallel lines,
intersecting lines
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Figure 3.4 House and stick figure
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Case Study: Design - Algorithm
• (no real data involved, so skip Data Requirements)
• For stick figure:1.Draw a circle.
2.Draw a triangle.
3.Draw intersecting lines.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 32
Case Study: Design - Algorithm
• (no real data involved, so skip Data Requirements)
• For stick figure:1.Draw a circle.2.Draw a triangle.
2.1 Draw intersecting lines.2.2 Draw a base line.
3.Draw intersecting lines.
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 33
Case Study: Structure Chart
Draw aCircle
Drawintersecting
lines
Draw abase
Draw aTriangle
Drawintersecting
lines
Draw afigure
Original Problem
Detailed
subproblems
Level 0
Level 1
Level 2
Subproblems
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 34
3.4 Functions without Arguments
• Functions important part of top-down design• main( ) is a function called by the OS• Form of call: fname( );• Example: drawCircle( );• Interpretation: the function fname is
activated. After fname finishes execution, the program statement that follows the function call will be executed next.
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Some Notes on Functions
• Don’t need to know details about how a function is implemented to know how to call.
• E.g.y = sqrt(x); // don’t know how sqrt implemented
• Do know how function is used (called).
• Empty parentheses indicate no arguments (more on this later).
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Function Prototype
• Declares the function to the compiler
• Appears before function main.
• Tells compiler the function’s type, its name, and information about arguments.
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Function Prototype (no Arguments)
• Form: ftype fname( );
• Example: void skipThree( );
• Interpretation: identifier fname is declared to be the name of a function. The identifier ftype specifies the data type of the function result. Ftype of void indicates the function does not return a value.
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Function Definitions
• Specifies the function’s operations
• Function header similar to function prototype
• Function body contains declarations for local variables and constants and executable statements
• Prototypes precede main function (after #include directives)
• Function definitions follow main function
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Function Definition (no arguments)
• Syntax: ftype fname( )
{
local declarations
executable statements
}
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Function Definition (no arguments)
• Example:// Displays block-letter H
void printH( )
{
cout << “** **” << endl;
cout << “** **” << endl;
cout << “******” << endl;
cout << “******” << endl;
cout << “** **” << endl;
cout << “** **” << endl;
} // end printH
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 41
Order of Execution
int main( )
{
drawCircle( );
drawTriangle( );
drawIntersect( );
return 0;
}
void drawCircle( )
{
cout << “ * “ << endl;
cout << “ * * “ << endl;
cout << “ * * “ << endl;
//return to calling function
} // end drawCircle
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Notes on Function Execution
• Execution always begins at first statement of main function
• When a function is called– space is set aside for function variables– statements of function are executed– control returns to statement following call– function ends with space released
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Function Advantages
• Team assignments on large project• Simplify tasks• Each function is a separate unit• Top-down approach• Reuse (e.g. drawTriangle)• Procedural abstraction• Information hiding
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Displaying User Instructions
• Simple functions (no arguments, no return value) are of limited use
• Useful for displaying instructions to user
• E.g.
void instruct( ); // prototype
…
instruct( ); //function call
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// Displays instructions to user of area/circumference program
void instruct (){
cout << "This program computes the area and " << endl;cout << "circumference of a circle. " << endl << endl; cout << "To use this program, enter the radius of the " << endl;
cout << "circle after the prompt" << endl; cout << "Enter the circle radius: " << endl << endl; cout << "The circumference will be computed in the same”
<< endl; cout << "units of measurement as the radius. The area "
<< endl; cout << "will be computed in the same units squared."
<< endl << endl;}
Figure 3.10 Function instruct
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Functions with Input Arguments
• Functions used like building blocks
• Build systems one function at a time– E.g. stereo components
• Use function arguments to carry information into function subprogram (input arguments) or to return multiple results (output arguments)
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Functions with Input Arguments
• Arguments make functions versatile
• E.g.:
rimArea = findArea(edgeRadius) -
findArea(holeRadius);
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void Functions with Input Arguments
• Give data to function to use
• Don’t expect function to return any result(s)
• Call format:
fname (actual-argument-list);
• E.g.:
drawCircleChar(‘*’);
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drawCircleChar(‘*’);
void drawCircle(char symbol)
{
cout << “ “ << symbol << endl;
cout << “ “ << symbol << “ “ << symbol << endl;
cout << “ “ << symbol << “ “ << symbol << endl;
} // end drawCircle
‘*’symbol
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Functions with Arguments and a Single Result
• Functions that return a result must have a return statement:
Form: return expression;
Example: return x * y;
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#include <iostream>#include <cmath>using namespace std;const float PI = 3.14159;float findCircum(float);float findArea(float);int main( ){ float radius = 10.0; float circum; float area; circum = findCircum(radius); area = findArea(radius); cout << “Area is “ << area << endl; cout << “Circumference is “ << circum << endl; return 0;}
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// Computes the circumference of a circle with radius r
// Pre: r is defined and is > 0.
// PI is a constant.
// Post: returns circumference
float findCircum(float r)
{
return (2.0 * PI * r);
}
// Computes the area of a circle with radius r
// Pre: r is defined and is > 0.
// PI is a constant.
// Post: returns area
float findArea(float r)
{
return (PI * pow(r,2));
}
Figure 3.12 Functions findCircum and findArea
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circum = findCircum(radius);
float findCircum(float r){ return (2.0 * PI * r);}
10
radius
10
r
62.8318
call findCircum62.8318
circum
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Function Definition (Input Arguments with One Result)
• Syntax:
// function interface comment
ftype fname(formal-parameter-declaration-list)
{
local variable declarations
executable statements
}
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Function Definition (Input Arguments with One Result)
• Example:// Finds the cube of its argument.// Pre: n is defined.int cube(int n){
return (n * n * n);}
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Function Prototype (With Parameters)
• Form:
ftype fname(formal-parameter-type-list);
• Example:
int cube(int);
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Function Interface Comments
• Preconditions– conditions that should be true before function is
called– // Pre: r is defined
• Postconditions– conditions that will be true when function
completes execution– // Post: Returns circumference
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Problem Inputs vs. Input Parameters
• Problem inputs– variables that receive data from program user– through execution of input statement
• Input parameters– receive data through execution of function call
statement– must be defined before function is called
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Listing 3.14: Testing function testScale.cpp
// File testScale.cpp
// Tests function scale.
#include <iostream>
#include <cmath>
using namespace std;
// Function prototype
float scale(float, int);
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int main(){ float num1; int num2;
// Get values for num1 and num2 cout << "Enter a real number: "; cin >> num1; cout << "Enter an integer: "; cin >> num2; // Call scale and display result. cout << "Result of call to function scale is " << scale(num1, num2) << endl; return 0;}
Listing 3.14: Testing function testScale.cpp (continued)
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// Multiplies its first argument by the power of 10
// specified by its second argument.
// Pre: x and n are defined and library cmath is
// included
float scale(float x, int n)
{
float scaleFactor; // local variable
scaleFactor = pow(10, n);
return (x * scaleFactor);
}
Listing 3.14: Testing function testScale.cpp (continued)
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float scale(float x, int n){ float scaleFactor; // local variable scaleFactor = pow(10, n); return (x * scaleFactor);}
cout << "Result of call to function scale is " << scale(num1, num2) << endl;
.
.
.
Formal parameters
Information flow
Actual arguments
Listing 3.14: Testing function testScale.cpp (continued)
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Argument/Parameter List Correspondence• Must have same number of actual
arguments and formal parameters• Order of arguments in the lists determines
correspondence• Each actual argument must be of a data type
that is compatible to the corresponding formal parameter
• The names of the actual arguments do not need to correspond to the formal parameters
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 64
Function Data Area
• Each time function is executed– an area of memory is allocated for storage of
the function’s data (formal parameters and local variables)
– it is created empty with each call to the function
• When the function terminates– the data area is lost
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Data Areas After Call scale(num1, num2);
Function main Data
Area
Function Scale Data
Areanum1
num2
x
n
scaleFactor
2.5
-2
2.5
-2
?
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Testing Functions Using Drivers
• Any function can be tested independently
• Test driver – defines values for the function’s arguments– calls the function– displays the value returned for verification
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Scope of Names• Scope - where a particular meaning of a
name is visible or can be referenced• Local - can be referred to only within the
one function– applies to
• formal argument names• constants and variables declared within the function
• Global - can be referred to within all functions– useful for constants– must be used with care
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Listing 3.15 Outline of program for studying scope of names
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Using Class string
• Data abstraction– facilitated in C++ through class feature– enables programmers to define new types– defines a set a values and a set of operations
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Accessing the String Library
• Must include the appropriate library
#include <string>
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String Objects
• Attributes include– character sequence it stores– length
• Common operations<< >> = +
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Listing 3.16 Illustrating string operations
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Listing 3.16 Illustrating string operations (continued)
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Declaring string Objects
• General declarations format:
type identifier1, identifier2, . . .;
• E.g.:
string firstName, lastName;
string wholeName;
string greeting = “Hello “;
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Reading and Displaying Strings
• Extraction operator is defined for strings
cin >> firstName; // reads up to blank or return
• Insertion operator is defined for strings
cout << greetings << wholeName << ‘!’ << endl;
• Can read string with blanks
getline(cin, lastName, ;\n’);
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String Assignment and Concatenation
• + puts strings together (concatenates)
• E.g.:
wholeName = firstName + “ “ + lastName;
• Note need for space between names
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Operator Overloading
• Note use of +– usually means addition for two numeric values– has been redefined (overloaded) to also mean
concatenation when applied to two strings
• Useful when defining new types
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Accessing String Operations• Member functions length and at• These functions can be called using dot
notation• Applies the identified operation to the
named object• E.g.:
wholeName.length( )returns the length of the string currently stored in the variable wholeName
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Dot Notation
• Syntax: object.function-call
• Ex: firstName.at(0)
this returns the character in firstName that is at position 0 (start numbering characters from left, beginning at 0).
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Additional Member Functions
• Searching for a stringwholeName.find(firstName)
• Inserting characters into a stringwholeName.insert(0, “Ms.”);
• Deleting portion of a stringwholeName.erase(10,4);
• Assign a substring to a string objecttitle.assign(wholeName, 0 3);
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Introduction to Graphics
• In normal computer output (called text mode), we use cout to display lines of characters to the standard output device, or console.
• Now we discuss another mode of output (called graphics mode) that enables you to draw pictures or graphical patterns on your computer screen.
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Windows and Pixels
• In text mode, you don’t pay much attention to the position of each line of characters displayed on the screen. In graphics programming, you control the location in a window of each line or shape that you draw. Consequently, you must know your window size and how to reference the individual picture elements (called pixels) in a window.
• You can visualize a window as an X-Y grid of pixels. If your window has the dimensions 400 x 300. The pixel at the top-left corner has X-Y coordinates (0, 0), and the pixel at the bottom-right corner has X-Y coordinates (399, 299).
• Notice the pixels in the Y-direction are numbered differently from how we are accustomed. The Y-coordinate values increase as we move down the screen. In a normal X-Y coordinate system, the point (0, 0) is at the bottom-left corner, not the top-left corner.
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Initializing a Window
• A graphics program is a sequence of statements that call graphics functions to do the work.
• Functions getmaxwidth and getmaxheight return the position of the last pixel in the X- and Y-directions on your computer screen. The statements
bigx = getmaxwidth(); // get largest x-coordinate.bigy = getmaxheight(); // get largest y-coordinate.initwindow(bigx, bigy, "Full screen window - press a character to close window");
pop up a window of maximum width and height with the third argument as the window label (see Fig. 3.13). The window position is set by the optional 4th and 5th arguments. If they are missing, the top-left corner of the window is at (0, 0).
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Listing 3.17 Draw intersecting lines
84
#include <graphics.h>#include <iostream> using namespace std; int main() { int bigx; // largest x-coordinate int bigy; // largest y-coordinate bigx = getmaxwidth(); // get largest x-coordinate bigy = getmaxheight(); // get largest y-coordinate initwindow(bigx, bigy, "Full screen window - press a key to close"); // Draw intersecting lines line(0, 0, bigx, bigy); // Draw white line from (0, 0) to (bigx, bigy) setcolor(LIGHTGRAY); // Change color to gray line(bigx, 0, 0, bigy); // Draw gray line from (bigx, 0) to (0, bigy) // Close screen when ready getch(); // pause until user presses a key closegraph(); // close the window // Display window size in console cout << "Window size is " << bigx << " X " << bigy << endl; return 0;}
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Fig. 3.13 Intersecting Lines
85
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Listing 3.18 Draw a House
86
#include <graphics.h> int main() { // Define corners of house int x1 = 100; int y1 = 200; // top-left corner int x2 = 300; int y2 = 100; // roof peak int x3 = 500; int y3 = 200; // top-right corner int x4 = 500; int y4 = 400; // bottom-right corner int x5 = 325; int y5 = 400; // bottom-right corner of door int x6 = 275; int y6 = 325; // top-left corner of door initwindow(640, 500, "House - press a key to close", 100, 50); // draw roof line(x1, y1, x2, y2); // Draw line from (x1, y1) to (x2, y2) line(x2, y2, x3, y3); // Draw line from (x2, y2) to (x3, y3) // draw rest of house. rectangle(x1, y1, x4, y4); // draw door. rectangle(x5, y5, x6, y6);
getch(); // pause until user presses a key closegraph(); // close the window return 0;}
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Figure 3.14 House
87
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Listing 3.19 Draw Happy Face
88
#include <graphics.h> int main() { int midX, midY, // coordinates of center point leftEyeX, rightEyeX, eyeY, // eye center points noseX, noseY, // nose center point headRadius, // head radius eyeNoseRadius, // eye/nose radius smileRadius, // smile radius stepX, stepY; // x and y increments initwindow(500, 400, "Happy Face - press key to close", 200, 150); // draw head. midX = getmaxx() / 2; // center head in x-direction midY = getmaxy() / 2; // center head in y-direction headRadius = getmaxy() / 4; // head will fill half the window circle(midX, midY, headRadius); // draw head.
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Listing 3.19 cont’d.
89
// draw eyes. stepX = headRadius / 4; // x-offset for eyes stepY = stepX; // y-offset for eyes and nose leftEyeX = midX - stepX; // x-coordinate for left eye rightEyeX = midX + stepX; // x-coordinate for right eye eyeY = midY - stepY; // y-coordinate for both eyes eyeNoseRadius = headRadius / 10; circle(leftEyeX, eyeY, eyeNoseRadius); // draw left eye. circle(rightEyeX, eyeY, eyeNoseRadius); // draw right eye. // draw nose. noseX = midX; // nose is centered in x direction. noseY = midY + stepY; circle(noseX, noseY, eyeNoseRadius); // draw smile. smileRadius = int(0.75 * headRadius + 0.5); // 3/4 of head radius arc(midX, midY, 210, 330, smileRadius);
getch(); closegraph(); return 0;}
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Figure 3.15 Happy face
90
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Listing 3.20 Paint a House
91
#include <graphics.h> int main() { // Insert same code as in Listing 3.18 (Draw a house)
... // draw rest of house. rectangle(x1, y1, x4, y4);
// Paint the house setfillstyle(HATCH_FILL, LIGHTGRAY); floodfill(x2, y2 + 10, WHITE); // Paint the roof setfillstyle(LINE_FILL, WHITE); floodfill(x2, y1 + 10, WHITE); // Paint the house setfillstyle(SOLID_FILL, BLUE); bar(x5, y5, x6, y6); // Draw blue door
getch(); closegraph(); return 0;}
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Figure 3.16 Painted House
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Listing 3.21 Draw Pirate
93
#include <graphics.h> int main() { // Insert same code as in Listing 3.19 (Draw Happy Face) . . .
// Draw nose noseX = midX; // nose is centered in x direction noseY = midY + stepY; circle(noseX, noseY, eyeNoseRadius);
// Draw frown smileRadius = int(0.75 * headRadius + 0.5); // 3/4 of head radius arc(midX, midY + headRadius, 65, 115, smileRadius / 2); // Draw frown setfillstyle(CLOSE_DOT_FILL, WHITE); pieslice(midX, midY, 10, 60, smileRadius); // Draw eye patch outtextxy(getmaxx() / 3, getmaxy() - 20, "PIRATE WITH AN EYE PATCH");
getch(); closegraph(); return 0;}
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Fig. 3.17 Pirate with eye patch